Turtle-- question for you regarding gender @14 weeks

Hi Turtle,
At 14 weeks 5 days I got an ultrasound and doctor told me it was a BOY since he saw scrotum and a penis. I do not have a picture though to show you. I was convinced it was a boy but now I'm starting to doubt if it was too early on my pregnancy to confirm this?? Today I am 17 weeks and I go back for another u/s at 20 weeks. Can I rest assured he is indeed a boy and buy blue? Thanks for your feedback and sorry to not post a pic. :-)